Revisiting the S-allele nomenclature in sweet cherry (Prunus avium) using RFLP profiles

Correct assignment of self-incompatibility alleles (S-alleles) in sweet che rry (Prunus avium L.) is important to assure fruit set in field plantings a nd breeding crosses. Until recently, only six S-alleles had been assigned. With the determination that the stylar product of the S-locus is a ribonucl ease (RNase) and subsequent cloning of the S-RNases, it has been possible t o use isoenzyme and DNA analysis to genotype S-alleles. As a result, numero us additional S-alleles have been identified; however, since different grou ps used different strategies for genotype analysis and different cultivars, the nomenclature contained inconsistencies and redundancies. In this study restriction fragment-length polymorphism (RFLP) profiles are presented usi ng HindIII, EcoRI, DraI, or XbaI restriction digests of the S-alleles prese nt in 22 sweet cherry cultivars which were chosen based upon their unique S -allele designations and/or their importance to the United States sweet che rry breeding community. Twelve previously published alleles (S-1, S-2, S-3, S-4, S-5, S-6, S-7, S-9, S-10, S-11, S-12, and S-13) could be differentiat ed by their RFLP profiles for each of the four restriction enzymes. Two new putative S-alleles, both found in 'NY1625', are reported, bringing the tot al to 14 differentiable alleles. We propose the adoption of a standard nome nclature in which the sweet cherry cultivars 'Hedelfingen' and 'Burlat' are (SS5)-S-3 and (SS9)-S-3, respectively. Fragment sizes for each S-allele/re striction enzyme combination are presented for reference in future S-allele discovery projects.